The present application relates generally to devices for applying light such as ultraviolet (“UV”) light to the cornea of the eye; to methods of manufacturing such devices; and to methods of applying phototherapy to the eye.
In humans and other mammals, the eye includes a clear, dome-shaped element referred to as the cornea disposed at the front of the eye. Light passes into the eye through the cornea and, after passing through other structures such as the iris and the lens of the eye, ultimately impinging on the retina. The light impinging on the retina is converted to neural impulses that are processed to form the visual images. The cornea and the lens refract the light passing through them. In a healthy eye, the refraction imparted by the cornea and the lens focuses the light on the retina.
Most of the light refraction required for the primary focusing on the retina is done by the cornea, with the lens making the accommodative changes to move focus from close to distant objects. Mismatches between the corneal curvature and the axial length of the eye, imperfections in the shape of the cornea, malpositions of the lens, and error in the vitreous of the eye can all lead to vision errors. For example, an eye that has a cornea that focuses the light in front of the retina (an eye with too much curvature relative to the axial length of the eye) suffers from myopia (also referred to as near-sightedness). Conversely, a cornea that is not curved enough for the axial length results in hyperopia (also referred to as far-sightedness), where the focal point is behind the retina. Astigmatism is an uneven curvature of the cornea with respect to the shape of the retina. All three conditions result in an out of focus image formed on the retina. Beyond these errors in curvature that affect healthy eyes, pathological conditions such as keratoconus and corneal ectasia result in unstable corneas and impaired vision.
Eyeglasses and contact lenses can correct conditions such as myopia, hyperopia and astigmatism by adding an artificial refractive element to the system. However, these devices impose some inconvenience on the patient. Accordingly, refractive surgical therapies such as radial keratotomy and laser ablation of the cornea have been developed. These procedures correct vision by reshaping the cornea so as to alter its refractive properties. However, these procedures have certain drawbacks and can have undesirable side effects.
In a technique known as orthokeratolgy, the cornea is mechanically reshaped by applying a rigid contact lens having a shape different from the existing shape of the cornea. The lenses are worn overnight. However, changes in shape induced by orthokeratology are temporary. They typically last only 24-48 hours, after which the cornea reverts to its original shape.
In yet another technique, the cornea can be reshaped by crosslinking fibers of collagen which form part of the cornea. The crosslinking can be performed by applying UV light to the cornea in conjunction with a chemical agent such as riboflavin. Typically, the UV light is applied by directing UV light from one or more light emitting diodes (“LEDs”) m into the patient's eye, substantially perpendicular to the surface of the cornea. The crosslinking strengthens the cornea and can also cause reshaping of the cornea Procedures of this type require that the patient keep the treated eye open for a prolonged period without blinking. This creates discomfort for the patient and also requires close monitoring by trained personnel to assure that the cornea remains hydrated.
It has also been proposed to apply crosslinking in conjunction with orthokeratology. In this approach, the crosslinking is performed after mechanical reshaping or while the cornea is held mechanically in the desired shape. The crosslinking acts to set the cornea and prevent reversion of the cornea to its original shape. For example, Mrochen et al., U.S. Published Patent Application No. 2008/0208177, proposes a thick, rigid mold equipped with an array of light emitting diodes or “LED's.” While the mold is applied to the cornea, the LED's emit UV light in the direction toward the surface of the cornea. The mold may include a diffuser plate interposed between the LED's and the cornea to make the light impinging on the cornea more uniform. In another variant, the array of LED's and the diffuser plate is replaced by a branching array of “optical light guides” extending to numerous points on the surface of the cornea. Structures of this type still require that the patient keep his or her eye open during the treatment, without blinking.
Chuck et al., U.S. Published Patent Application No. 2013/0211389, discloses a treatment device which incorporates radiation-emitting elements such as LEDs, along with the circuitry required to drive these elements, into a device having size and shape resembling a conventional contact lens. Using this device, the patient can blink or keep his or her eye shut while receiving crosslinking therapy. This provides a more comfortable patient experience, greatly reduces the risk of corneal dehydration during the therapy, and also reduces the need for constant monitoring of hydration by medical personnel. However, LEDs and circuitry incorporated into the device evolve heat during operation. Therefore, the power which can be applied by the device must be restricted.